# Mysql Compatibility

+ Does not support FULLTEXT, HASH and SPATIAL
+ Descending indexes are not supported
+ Unable to add PRIMARY KEY of type CLUSTERED to the table
+ Deleting a PRIMARY KEY of type CLUSTERED
+ An optimizer switch like the one provided in MySQL is not supported, and all invisible indexes can be made visible again: `use_invisible_indexes=on` 
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MySQL compatibility
- FULLTEXT, HASH and SPATIAL indexes are not supported.
- Descending indexes are not supported (similar to MySQL 5.7).
- Unable to add PRIMARY KEY of type CLUSTERED to the table.
- Deleting PRIMARY KEY of CLUSTERED type is not supported.
- The optimizer switch use_invisible_indexes=on provided in MySQL resets all invisible indexes to visible. This feature is not available in TiDB.